Supercomputers and other large computer systems typically include a large number of processors housed in cabinets arranged in banks. FIG. 1, for example, illustrates a large computer system 100 configured in accordance with the prior art. The computer system 100 includes a plurality of computer cabinets 102 (identified individually as computer cabinets 102a-d) situated on a floor 103. Each of the computer cabinets 102 contains a plurality of computer modules 106 arranged vertically in close proximity to each other. Each of the computer modules 106 can include a motherboard carrying one or more processors, buses, and associated memory. The computer modules 106 are positioned close together for a number of reasons. One reason is that close proximity can increase computational performance by increasing signal speed and reducing signal decay. Another reason is that close proximity can reduce cable cost and routing complexity. One downside of arranging the computer modules 106 in close proximity, however, is that they can generate considerable heat during operation that can result in damage or reduced performance if not dissipated.
To dissipate the heat generated by the computer modules 106, the computer system 100 further includes an air conditioning unit 110. The air conditioning unit 110 includes a cooling coil 112 and two air movers 114. In operation, the air conditioning unit 110 draws in warm air from around the computer cabinets 102 and cools the air before flowing it into a plenum 104 extending beneath the floor 103. The plenum 104 distributes the high pressure cooling air to the computer cabinets 102. Fans 130 positioned toward the top of the computer cabinets 102 draw the cooling air upward through the computer cabinets 102 to cool the computer modules 106. Warm air from the computer cabinets 102 then circulates back to the air conditioning unit 110 as part of a continual cooling cycle.
One shortcoming associated with the computer system 100 described above is that the computer cabinets 102 receive a non-uniform distribution of cooling air from the air conditioning unit 110. The non-uniform distribution of cooling air can result from the placement of the computer cabinets 102 relative to the air conditioning unit 110 and other reasons. As a result of this imbalance, the computer modules 106 in the computer cabinet 102a may not be sufficiently cooled, while the computer modules 106 in the computer cabinet 102d may be receiving more cooling air than is necessary for sufficient cooling.
One way to overcome this problem is to increase the flow rate of cooling air from the air conditioning unit 110. This approach is often impractical, however, because of the high cost of constructing and operating such high-capacity air conditioning systems. Further, this approach often requires larger fans, increased coolant flows, and higher power requirements than the computer facility was originally designed to accommodate. In addition, such systems are typically very noisy, creating a difficult work environment for facility personnel.
Another way to improve the cooling characteristics of the air conditioning system described above is to construct ducts (not shown) between the floor plenum 104 and individual computer cabinets 102 in an effort to balance the air flow between cabinets. While theoretically possible, in practice this approach is extremely difficult for large computer systems because of the many variables involved. For example, the addition or removal of a single computer cabinet 102 could disturb the balance of the entire system, requiring readjustment of the ducting to rebalance the air distribution.
A further approach to improve the cooling characteristics of the air conditioning system described above is to reduce the temperature of the cooling air provided by the air conditioning unit 110 in an attempt to compensate for the non-uniform air distribution. This approach is often impractical as well, however, because it typically requires lowering the air temperature below the dew point in the air conditioning unit 110, causing water vapor to condense out of the air. The removal of water vapor can lower the relative humidity to such a point that electrostatic discharge becomes a concern in the facility. As a result, water vapor may have to be added back into the facility air to bring the relative humidity back up to an acceptable level.